Alkylation of aromatic compounds with a C2 to C4 olefin and transalkylation of polyalkylaromatic compounds are two common reactions for producing monoalkylated aromatic compounds such as cumene and ethylbenzene. Examples of these two reactions that are practiced industrially to produce cumene (isopropylbenzene) are the alkylation of benzene with propylene and the transalkylation of benzene and a diisopropylbenzene (DIPB). The alkylation reaction forms cumene and common byproducts such as DIPBs and triisopropylbenzenes (TIPBs). DIPBs, TIPBs, and some of the higher polyisopropylbenzenes can be readily transalkylated by benzene to produce cumene. Alkylation and transalkylation reactions may be combined in one process unit in a single reaction zone or multiple reaction zones.
Many aromatic alkylation catalysts containing a variety of zeolites have been proposed and used for alkylating and transalkylating aromatics. Regardless whether the reaction is alkylation or transalkylation, it is important that such catalysts exhibit acceptable activity to convert the reactants and acceptable yield to the desired product. Although compounds containing nitrogen may be used in the synthesis and/or treatment of such zeolites, nitrogen is known to reduce the activity of the resulting catalysts. Therefore it is well known in the art to remove nitrogen such as by heating for sufficient time and temperature to obtain the hydrogen form of the zeolite. It is also known that nitrogen compounds in the reactants may be adsorbed on the active catalyst sites and cause rapid deactivation of the catalyst. The effect of nitrogen on the selectivity of such catalysts is inconsistent as both increased and decreased selectivity has been reported. The source or sources of the inconsistent selectivity changes is uncertain as differences in one or more variables, such as, types of zeolites, zeolite treatments steps, catalyst compositions and preparation steps, the reactants, desired products, and various reaction conditions have been reported.
Catalysts having superior yield are desirable because they may be used to reduce the construction and/or operating costs of a process unit since recycle and waste streams are reduced. At the same time, the catalyst activity and stability must be maintained at levels sufficient to avoid eliminating the benefit conferred by the increased yield. It is desired that the activity and stability be sufficient to enable use of the catalyst in existing processing units.